It has been a tough period for De Gea, who endured an error-riddled end to the Premier League season with United.
Speaking to reporters after Spain moved five points clear in Group F, Kepa said: "I'm going to continue working as I have until now, doing my best at my club to keep the confidence of the coach.
"Whoever plays will do very well. Of course I understand that David is sad, we all train to play and then it is the decision of the coach, and it is up to you to respond well."
"We are always surrounded by such controversies,” the 24-year-old continued. “But we must take it naturally. I'm happy to play, to help the team and to finish the season in the best way possible.
"The season has been very long, but before we left we had these two very important commitments. We are happy to finish in the best way possible."
The Chelsea man was keen to stress that his inclusion in the side over De Gea has not caused any strain between the two men.
"I have a great relationship with David," Kepa continued. "We train a lot of the time together apart from the team, as well with Pau Lopez, because we are keepers.
"We have a relationship from many years ago and we don't need to say anything to each other to help each other."
Asked if he feels like Spain's number one keeper, Kepa added: "I just felt tonight because I am not feeling the main goalkeeper now.
"I am just one more out of the three keepers Luis Enrique has been calling in and when I have the chance of playing I try to add my experience to the team."
Indeed, Spain assistant boss Robert Moreno explained that the number one spot is still up for grabs. "We don't think the De Gea period with Spain is over,” he told reporters. “But Kepa had an incredible end of the season – champion of the Europa League with great performances. In this concrete moment, we thought that Kepa could help us in a better way."
While there are no more matches for Spain until September, De Gea must now face the rumours regarding his future at United, amid speculation he could leave Old Trafford this summer, if he does not sign an extension to his contract, which has just 12 months to run.